This disclosure relates generally to the field of digital photography. More particularly, it relates to techniques for the capture and processing of high dynamic range images when appropriate for the scene. As used herein, the terms digital camera, digital imaging system or device and the like are meant to refer to any device, apparatus or system that has the ability to capture digital images (still and video).
Today, many personal electronic devices come equipped with digital cameras. Illustrative personal electronic devices include, but are not limited to, mobile phones, personal data assistants, portable music players, laptop computer systems, desktop computer systems, tablet computer systems and wearable electronic devices such as watches and glasses. Image sensors used in these types of devices often have relatively small dynamic ranges. That is, their ability to capture a range of light from total darkness to full sunlight in a single image is limited. Consumer-grade sensors often provide only 8-10 bits resolution. Such sensors can distinguish between 256-1024 different brightness levels (assuming no noise); generally an insufficient number to adequately represent the range of light to which they are exposed. One result of a scene exceeding the sensor's/camera's dynamic range is that pixels are clipped. As the number of clipped pixels increase, there comes a point where the image becomes unpleasant to look at.
High dynamic range imaging (HDRI or HDR) is a set of techniques used by digital capture systems to reproduce a greater dynamic range than is possible using standard single image capture techniques. In particular, HDR images are generally achieved by capturing multiple standard images, often using exposure bracketing in which each image is captured with a different exposure value, which are then merged into a single HDR image. While providing images with an extended dynamic range, these operations do not come for free. When trying to fuse individual captures having different exposure levels into an HDR image, it is very difficult to avoid ghosting when there is subject motion in the scene, even when advanced de-ghosting techniques are used. This is a fundamental limitation of exposure bracketing HDR operations. Because of this limitation, it can be important to employ HDR techniques only when needed.